Acyloxyalkanesulfonates are anionic surfactants used as base materials for syndet soaps, cosmetic compositions and cleaning formulations. Their features include good foaming properties, good hard water stability and good skin compatibility.
Disadvantages of the use of these surfactants are that the majority of them are brittle solids which are stirrable or melt only at high temperatures. At these high temperatures required just to make it possible to process the acyloxyalkanesulfonate the latter is highly sensitive to oxidation; thermal decomposition begins, and discoloration occurs.
Accordingly, it is advantageous to lower the melting point or the temperature at which the acyloxyalkanesulfonates are stirrable and can thus be processed. To solve this problem it has already been disclosed to prepare acyloxyalkanesulfonates of this type comprising mixed salts, i.e. where the cation consists of a mixture of two different cations, for example sodium and potassium ion (U.S. Pat. No. 3,029,264). These acyloxyalkanesulfonates, which are preferably acyloxyisethionates, are prepared by esterifying fatty acids with a salt of isethionic acid. If, then, in accordance with the details of this prior art, a mixture of Na isethionate and K isethionate is employed, the esterification with the fatty acid can be conducted at just 150 to 160.degree. C. This makes it possible to avoid the development of discoloration. With this process, however, equimolar amounts of fatty acid and isethionate are reacted in every case. It has now been found that in the case of such acyloxyalkanesulfonates having mixed cations it is possible to reduce still further the stirrability limit, i.e. the temperature at which the product can still just be stirred, if rather than equimolar amounts an excess of fatty acid is employed.
Acyloxyalkanesulfonates with mixed cations have also been described in WO 94/09107. In that document, however, there is no indication as to the effects of the mixed cations on the preparation conditions.